Our present understanding of segmental motor control has been greatly influenced by investigations of the lumbosacral spinal cord and hindlimb muscles of the cat. While such a focus has been of great benefit towards the understanding of motor behavior in general, it may also result in a potentially limited view of the segmental motor control system. At different levels of the neuraxis, there are potentially different strategies for the control of muscle force. For a fuller understanding of the segmental motor control system, this project focuses on one aspect of this system in the cat forelimb. The main objective of this project is to determine how the motoneuron and muscle unit portions of single distal forelimb motor units interact to modulate muscle force. This will be accomplished by using electrophysiological techniques. Our long-term objective is to conduct a thorough investigation of the cervical spinal cord and muscles of the cat forelimb. Hopefully, this effort will contribute to our understanding of the synaptic organization of distal forelimb motor units and how muscle force is controlled through their recruitment and rate modulation. Furthermore, it should be possible to determine what organizational principles are common between the forelimb and other areas of motor organization, and what specializations are unique to the forelimb because of the motor tasks it must perform. Without a clear understanding of the basic properties and design features of the segmental motor control system at all levels of the neuraxis, we will not be able to fully understand how this system is affected under a variety of neurological and injury-related disorders.